docs: def existing(self):
          """ find existing content assigned to this layout"""
          catalog = api.portal.get_tool('portal_catalog')
          results = []
          layout_path = self._get_layout_path(
              self.request.form.get('layout', '')
          )
          for brain in catalog(layout=layout_path):
              results.append({
                  'title': brain.Title,
                  'url': brain.getURL()
              })
          return json.dumps({
              'total': len(results),
              'data': results
          })